(a) Technical Field
The present invention relates to an apparatus for preventing deformation of a plastic battery pack case for an electric or hybrid vehicle. More particularly, it relates to an apparatus for preventing deformation of a plastic battery pack case, mounted on a lower portion of a vehicle, after compression molding.
(b) Background Art
In general, a battery pack case assembly mounted in a vehicle, and more particular in an electric or hybrid vehicle includes a battery pack, a battery management system, a blower, an upper cover, a lower case, structure reinforcing members, etc. While the upper cover does not receive a load and thus can be formed by a typical plastic composite molding process, the lower case and the structure reinforcing members are formed of steel formed by press molding to bear the load of a battery received in the case.
However, a technique for replacing the steel material of the existing lower case with a plastic composite material has been developed to reduce the weight of the vehicle, which is disclosed in U.S. patent application Ser. No. 13/039,806. A plastic battery pack case 1 for an electric vehicle, which is formed of a plastic composite material, typically has an upwardly open box structure. As shown in FIG. 1, the plastic battery pack case 1 comprises a case body 2, which accommodates various components required for the operation of an electric vehicle battery including a plurality of battery packs, and a mounting portion 3, which projects from the edge of the case body 2 to the outside and is fastened to the lower portion of the vehicle through insert-molded nuts. The plastic battery pack case 1 is mainly formed of a composite material comprising a matrix containing polyamide and polypropylene and reinforced with glass fibers and carbon fibers by a compression molding process.
Moreover, the plastic battery pack case 1 may be formed by an in-line compounding/extrusion deposition and molding process as disclosed in U.S. Pat. Nos. 6,444,153B1 and 6,165,604A.
However, the polyamide and polypropylene mainly used in the matrix are semi-crystalline polymers and deformed by contraction of the polymer matrix after molding. Such deformation is related to the degree of crystallization of the material depending on the thermal history. After compression molding, heat transfer does not occur uniformly in the plastic battery pack case, and thus a difference in cooling rate occurs to produce a tension in the cooling solid, thereby causing deformation. Therefore, the compression-molded plastic battery pack case 1 is deformed by contraction after compression molding, and thus it is difficult to ensure the proper internal space for mounting the case, which makes it difficult to easily mount the battery packs.
In other words, as the battery pack case 1 contracts in the longitudinal and width directions after compression molding, the internal space for accommodating the battery packs is reduced, and thus it is very difficult to mount the battery packs in the case.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.